Wave guide output window



Filed Nov. 29', 1957 L. M. W lNSLOW E L wAviz GUIDE OUTPUT WINDOW 2 Sheets-Sheet 1 IIIIIIIIIIIII INVENTORS LESTER M. W/NSLOW HERBERT J SHAW BY //M7 M ATTORNEYS REFLECTION COEFFICIENT MAGN/TUDE March 15, 1960 L. M. WINSLOW ETA!- WAVE GUIDE OUTPUT WINDOW Filed Nov. 29, 1957 2 Sheets-Sheet 2 .6 .5 3 .4 m S g .3 Q 3 L 143 kMc 7/ K J A v INVENTORS. 0 7 LESTER M. m/vsww 8.0 as 9.0 9.5 /0.0 HERBERT J SHAW FREQUENCY //v kMc BY fwd 7: 5M kgfizsm ATTORNEYJ WAVE GUIDE OUTPUT wnvnow Lester Marion Winslow, Stanford, and Herbert John Shaw, Palo Alto, Calif., assignors to Research Corporation, 7 New York, N .Y., a corporation of New York Application November 29, 1957, Serial No. 699,729

2 Claims. (Cl. 333-98) The present invention relates to output windows for evacuated ultra-high frequency electron discharge devices and the like and, more particularly, to a vacuum sealing means for high power electron tubes which will efiiciently transmit high frequency electromagnetic energy.

Recent developments in the high power tubes for the three centimeter wavelength region have created a need for output windows capable of transmitting peak power in excess of one megawatt and average power in the neighborhood of one kilowatt. Such windows are used in the output waveguides of high-power tubes to allow transmission of RF power from the evacuated output cavities of the tube to a pressurized external circuit.

It has been found that a dielectric element may be employed which can be made transparent to the RF wave by suitable impedance matching. In the prior art such has been accomplished by shaping the dielectric, as, for example, in tapered cone windows and stepped windows, or by utilizing matching sections separate from the dielectric.

The present improved window structure, which may be referred to as a filter window, uses separate matching elements with overall structure suitable for use as a three-element bandpass filter for broad band operation. The filter window of the present invention comprises resonant elements including resonant metal blocks and a resonant ceramic slab. The ceramic block has a specific loaded Q which is determined by the dielectric constant of the ceramic material, center frequency, and waveguide dimensions. The resonant blocks maybe designed to have a specified resonant frequency.

It is an object of the present invention to produce an output window for high power electron tubes capable of efiicient broadband transmission.

Another'object of the invention is to produce a waveguide window which is vacuum tight and able to withstand large thermal stress and mechanical stress due to the inherent pressure differentials of the pressurized system. Still another obj e'ctof the invention'is to roduce waveguide apparatus for use in 'a high power electron tube designed to function in the three centimeter wavelength region which is imp ervious'to damage by high energy electron bombardment originating in the output cavity of the tube.

1 Still afurther objectof the invention is to produce a device for the transmission of electromagnetic energy which is easy to construct and is compact in size;

These and other objects and advantages are achieved by a construction wherein a ceramic element is employed as the sealing unit at the output end of the device and the remainder of the filter window assembly includes matching metalblocks which establishes the desired electrical impedn'ance characteristi'c'swhile providing a means for eifectively shielding the ceramic element from the deleterious effects of high energy electron bombardment.

The principles of the present invention and other objects and advantages thereof will become more apparent from the following detailed description of the apparatus which will be more completely described with reference to the accompanying drawing, in which:

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reference numeral 10, having parallel top and bottom walls 12 and 14, respectively, and parallel side walls 16. The section of the waveguide 10 is provided at each end with flanges 18 and 20 having suitable apertures 19 formed therein to accommodate the insertion of fastening means for appropriately securing the waveguide structurev to associated apparatus.

The filter window structure illustrated in Figs. 1 and' 2 includes an essentially three-section filter having a low insertion loss and an excellent passband. One of the Tensile strength ..p.s.i. 26,000-28,000 Compressive strength p.s.i 260,000-285,000 Modulus of elasticity p.s.i 39,000,000 Flexural strength p.s.i 45,000-47,500" Water absorbtion percent 0 Specific gravity 3.64 Color White- Maximum working temperature C. 1600 Hardiness v Mohs scale 9 Specific heat B.t.u./lb 0.187' 1 THERMALCONDUCTIVITY F. i 11.8 400 'F. 15.6 ..800 FL 20.0 120091 1 23.0v wer j 1v -4 THERMAL COEFFICIENT OF LINEAR EXPANSION 25- 200 c. e 5.7 10 200- 400 C. a a 7.8 l0- 400- 600 C. I 8.9 10- 600-800 C. n l0.4 10 800-1000 C. 11.6 10'" ELECTRIC rno'rfnnrrns r 10 KMC.

. Temp. Dielectric Dissipa- Loss 4 Constant tionFactor Factor 9. 53 5. 5X10 5. axis- 9. s7 5. 0x10- 4. axis- 9. 70 4. 8 l0- 4. 6X10"! 9. 74 4.3 10- 4. 2x10- 9. 77 3.8)(10 3. sxm- 9. s1 3. 8Xl0' 3. 7x10- 9. s5 4. 0 .0- 3. s 10 9. 8B 4. zxlo- 4. 1 1o 9. 9o 5. 0 10- 4. 9x10- sections is comprised of a ceramic slab or dielectric plug 22 which is opaque to gases and translucent to electro magnetic waves. The material employed for the dielectric plug 22 should be a high strength, vacuum tight,

nongassing, low-loss ceramic. It has been found that satisfactory results may be achieved by employing a dielectric material such as WESGO AL-300 which is distributed by the Western Gold and Platinum Works, San Francisco, California. This material contains 97% A1 0 and has the following properties:

WESGO AL 300 A1 0 content 97 percent 

